When a web, such as a paper or board web, is wound in so-called center-drive winders, it is typical that the rolls that are formed are supported partly from the roll face by circumferential support against the support roll and partly by means of center support by means of seats fitted in the hole in the spool that constitutes the core of the roll. With respect to the prior art related to this, reference is made, for example, to Finnish Patent No. 79,505.
In the prior art solutions, the force of contact of the roll that is being produced against the support roll must often be limited to about 4 kN per meter of roll to about 8 kN per meter of roll width, depending on the paper grade. For example, the weight of a roll of a diameter of 1.5 m may produce a force component of about 20 kN per meter in the direction of the support roll. In such a case, by means of the seats, about 16 kN per meter must be carried. Since, in connection with a large diameter, large roll widths also occur, for example more than 3 m, the support forces at the seats can be even up to 25 kN. In order to avoid spool damage arising from a high seat load, it is necessary to use high-quality special spools of sufficiently large diameters. This again increases the costs of the spools compared with the rolls produced by means of winders of a different type.
As a rule, the prior-art center-drive winder solutions are provided with a drive system acting upon the seats. By means of the torque of the seats, the paper that is wound onto the roll that is being produced is tightened. It is a drawback of this method that the effect of the torque is reduced when the diameter of the paper layer wound onto the circumference of the roll becomes larger. The circumferential force produced with an invariable torque is inversely proportional to the diameter of the roll and is, thus, reduced when the roll becomes larger. Since the strength of the spools limits the torque that can be transferred from the seats, the employment of this method provides just limited help in the control of the roll tightness when large rolls are produced. A further problem of the center drive is the wide range of speeds of rotation that must be controlled by means of the drive gear.
Also, from the prior art, winders are known in which rider roll devices are employed in order that a sufficient pressure could be produced against the support roll in the initial stage of the winding and in order to prevent bending of the spool. During winding of certain paper grades, it has also proved advantageous to employ rider rolls to press the roll throughout the whole winding process.
With respect to the prior art, reference is also made to International patent application PCT/EP93/00140 (WO 93/15988), wherein a device is described for winding a paper or board web, in which device, in view of improving the quality of the lateral rolls, an additional drive gear placed at each side of the winder is used for the lateral rolls, which additional drive gear consists of a roll or belt on which a rotating drive unit of its own is fitted, which unit applies pressure elastically, substantially in the radial direction in relation to the support roll of the winder, against said lateral roll, the axis of rotation of said drive roll or belt being parallel to the axis of the support roll.
With respect to the prior art, reference is also made to FI Patent No. 74,260, in which a solution of a support belt that is fitted in a drum winder is described. From this patent, a winding arrangement is known for winding a moving web, in which arrangement there are support members for supporting the roll that is being formed at least primarily by means of circumferential support and loading members for keeping the roll against the support members, said support members comprising a carrier roll and a mobile support belt member, which supports at least a large roll over a considerable length of the circumference.